Three basic switching power supply topologies commonly used are buck converter, boost converter, and buck-boost converter. Of these, the simplest and most common is the buck converter. Various methods have been used to control buck converters in order to maintain an accurate and stable output voltage. Three of the most common methods to control buck converters are hysteretic control, pulse width modulation (PWM), and constant on-time (COT).
For buck converters, single-phase voltage-mode hysteretic control, also called “bang-bang” control or ripple regulator control, typically maintains an output voltage within a hysteresis band centered about an internal reference voltage. If the output voltage reaches or exceeds the reference voltage plus one-half of the hysteresis band, the controller turns OFF the high-side switch, typically a Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET), and turns ON the low-side switch, to block energy from being transferred from an input to an output. This latter condition is a power stage OFF-state, and causes the output voltage to decrease.
When the output voltage is at or below the level of the reference minus one-half of the hysteresis band, the power stage goes into ON-stage, and the controller turns ON the high-side switch, and turns OFF the low-side switch to allow energy transfer from the input to the output, which causes the output voltage to increase. This hysteretic method of control keeps the output voltage within the hysteresis band around the reference voltage.
The two most common control methods for switching boost converters are: 1) fixed-frequency voltage-mode or current-mode; and 2) gated-oscillator. Hysteretic control for boost converters has typically not been possible.